1. Field of the Invention
The invention relates to a method of forming multi-V-grooved sheet metal pulleys from a flat sheet metal strip. More particularly, the invention relates to a method of circular forming sheet metal pulleys by passing a flat sheet metal strip through a series of roll forms which produce the desired pulley configuration having a bottom wall hub integral with a multi-V-grooved side wall.
2. Description of the Prior Art
Many procedures have been used and are known for the formation of V-groove sheet metal pulleys from flat sheet metal. Many of these procedures involve stamping and drawing operations of sheet metal discs to produce cup-shaped blanks from which V-groove pulleys are subsequently roller spun. The finished V-groove pulleys or the cup-shaped stage blanks for subsequent spinning into V-groove pulleys which are produced by such prior stamping and drawing methods are not in balance dynamically since the pulleys and blanks are formed by series of progressive die steps on a non-rotating blank. Likewise, such stamped and drawn blanks and pulleys require a thicker starting disc or strip due to the uneven thinning of the metal in critical areas of the formed V-grooves.
Many of these problems have been eliminated by directly spinning the cup-shaped blanks and V-groove pulleys from flat sheet metal discs or cup-shaped stage blanks as shown in U.S. Pat. Nos. 1,680,061, 1,728,002, 2,869,223 and 3,852,863. Pulleys formed by these known spinning methods also require thicker starting blanks than desirable as in the stamping and drawing methods, due to the tension stretching and thinning in the metal of the groove walls during the spin forming of the V-grooves.
These known spinning and stamping methods for making V-groove pulleys also do not permit the satisfactory economical manufacture of a pulley with more than three grooves when formed from a single sheet metal blank. U.S. Pat. No. 3,852,863 only provides a method for the spinning of three grooves in a cylindrical cup-side wall of a pulley blank and may involve problems when used for the spinning of four or more grooves in a single blank.
Multiple groove pulleys having more than three grooves have been proposed or used wherein the grooves have been formed singularly or in pairs in separate sheet metal blanks and the separate grooved members then have been assembled to provide the final grooved pulley product having multiple grooves, such as shown for example in U.S. Pat. Nos. 1,700,416, 1,995,907, 2,008,300 and 2,092,571. Such procedures require additional assembling steps increasing considerably the production cost of the multi-V-groove pulleys.
Existing spinning procedures also do not enable a multi-V-groove pulley to be formed satisfactorily in which one or more of the V-grooves are offset in a radial direction with respect to others or when the V-grooves have different cross-sectional configurations on the same pulley.
Pulleys also have been formed by circular forming methods wherein a flat metal strip is passed through a series of forming rolls to form an annular grooved member. Examples of such procedures are shown in U.S. Pat. Nos. 1,641,440, 2,730,795 and 3,838,485. All of these known circular forming methods only form a single or double V-groove rim and require a separate hub flange wall to be attached thereto, which forms a two-piece sheet metal pulley. To form a multi-V-groove pulley having four or more V-grooves by these known methods it would require assembling the separately formed components together in an axial cylindrical arrangement. Likewise, a separate pulley hub bottom wall have to be attached thereto, as shown in U.S. Pat. No. 3,838,485. Again, such additional assembling of a plurality of separate components increases considerably the cost of producing such pulleys on a mass production basis.
Problems also are encountered in the circular forming of multi-groove annular members where the individual members are formed from convolutions of a continuous helix, such as shown in Pat. Nos. 1,753,586, 2,492,967, 3,001,496, 3,172,787, 3,797,088 and 3,838,485. The widths of the grooved strip required for the formation of a plurality of V-grooves is such that the distance that the ends of the severed convolution must be moved for alignment prior to joining is substantial, thereby placing an undesirable twisting tension on certain portions of the grooved annular rim.
There, thus, has been an existing need for a procedure for the circular forming of sheet metal pulleys having the hub flange bottom wall formed integrally with the cylindrical or annular V-grooved side wall, eliminating the additional procedures heretofore required of attaching a hub flange bottom wall to a circularly formed V-groove rim. Likewise, there has been a need for an economical procedure for the circular forming of multi-grooved pulleys having at least four V-grooves formed adjacent one another in a single sheet metal blank to eliminate the assembling of multiple components heretofore required.